Heretofore electrodes for use in electrolytic reactions have been formed from a wide variety of electrically conductive materials and provided in a wide variety of configurations. For efficient commercial utilization it is, of course, essential that the electrode be capable of extended usage without loss of its dimensional integrity. Electrode replacement when necessary commonly has required the complete shutdown of the electrolytic process and often a substantial expenditure of capital to provide the replacement electrode. Accordingly, electrode selection and expense commonly have had a large economic impact in many electrolytic processes.
Electrodes composed of block or fibrous carbon long have been known. Representative disclosures of the use of carbon fibers in electrolytic cells include U.S. Pat. Nos. 3,071,637; 3,072,558; 3,214,647; 3,459,917; 3,471,383; 3,476,604; 3,619,382; 3,637,468; 3,759,805; 3,764,499; 3,811,943; 3,827,964; 3,829,327; 3,852,113; 3,915,822; 3,923,629; 3,953,313; 4,046,663; 4,046,664; 4,061,557; 4,108,754; 4,108,755; and 4,108,757; and British Pat. Nos. 1,147,853; 1,240,793; 1,244,711; and 1,434,824. It has been recognized, however, that if carbon is used as an anode in an electrochemical cell such carbon is subject to an oxidative attack which leads to its complete destruction over a period of time which tends to be directly related to the cross-sectional area. Accordingly, such destruction commonly occurs at a relatively rapid rate if the carbon is present in a fibrous configuration and employed as an anode rather than a cathode. See U.S. Pat. No. 3,471,383.
Heretofore, dimensionally stable anodes for use in such environments commonly have been of relatively low surface area and formed all or in part from expensive noble metals or from an electrically conductive substrate such as graphite or a titanium metal base which bears a protective coating. While the noble metal electrodes commonly possess the desired stability, undesirable overvoltage characteristics are commonly exhibited. See, for instance, U.S. Pat. No. 3,446,607 wherein a block of graphite is coated with iridium, or U.S. Pat. No. 3,632,498 wherein a block of an electrically conductive base is coated with a mixed crystal material (e.g. oxides of ruthenium and titanium). Any break in the protective coating would provide an opening for the destruction of a graphite substrate or result in the formation of a non-conductive titanium oxide coating on a titanium base. Heretofore, anodes commonly have been commercially utilized in the chlor-alkali industry wherein expanded titanium metal bears an appropriate protective coating. Such coated titanium anodes have been found to be superior to carbon electrodes in that they exhibit relatively long useful lives. However, such electrodes have been of relatively low surface area (e.g. below about 25 cm.sup.2 /cm.sup.3 and commonly below 3 cm.sup.2 /cm.sup.3).
There has remained a need for a dimensionally stable anode of relatively high surface area. Such high surface area necessary for optimum contact with the electrolyte would appear to require a relatively frail structure which would be expected to militate against the desired dimensional stability necessary for extended usage.
It is an object of the present invention to provide a novel anodically stable relatively high surface area electrode.
It is an object of the present invention to provide an anode comprising carbon fibers which is capable of retaining its dimensional stability during extended periods of use.
It is an object of the present invention to provide an anode comprising carbon fibers which exhibits substantial stability when used in an environment in which oxygen is evolved.
It is an object of the present invention to provide a relatively high surface area anode which is capable of being produced on a relatively economical basis.
It is an object of the present invention to provide an anode which particularly is suited for usage in the removal of harmful contaminants from waste streams, even when present in relatively low concentrations.
It is a further object of the present invention to provide a relatively high surface area anode of relatively long life having relatively low overvoltage characteristics.
It is another object of the present invention to provide a dimensionally stable anode which during operation necessitates a lower energy consumption because of its relatively high surface area which enables the cell to be operated at a lower voltage.
These and other objects, as well as the scope, nature, and utilization of the present invention will be apparent to those skilled in the art from the following detailed description and appended claims.